We plan to isolate, purify, and partially characterize the macromolecular bone resorption stimulating agent(s) known as osteoclast activating factor (OAF). The factor(s) will be isolated by physical and chemical methods from culture medium of phytohemaglutinin-stimulated human peripheral leukocytes and assayed for the ability to stimulate bone resorption in organ culture. Chemical characterization of the purified factor(s) will include initially amino acid and carbohydrate composition, end group analysis and, if sufficient material is available, amino acid sequence. BIBLIOGRAPHIC REFERENCES: Raisz, L.G., C.L. Trummel, G.R. Mundy, and R.A. Luben, Immunologic Factors Influencing Bone Resorption: Role of Osteoclast Activating Factor from Human Leukocytes and Complement Mediated Prostaglandin Synthesis, in "Calcium Regulating Hormones," R.V. Talmage, M. Owen, and J.A. Parsons (eds), Excerpta Medica 1975, pp. 149-153. Luben, R.A., and D.V. Cohn, Effects of Parathormone and Calcitonin on Citrate and Hyaluronate Metabolism in Cultured Bone, Endocrinology 98:411-417 (1976).